In recent years, electrically powered vehicles such as electric vehicles, hybrid vehicles, fuel cell vehicles and the like have been developed into practical use as environmentally friendly vehicles. These electrically powered vehicles are each mounted with a motor generating force for driving the vehicle as well as a power supply system configured to include a power storage device supplying electric power for driving the motor. The hybrid vehicle is configured to be also able to travel by directly or indirectly using the output energy of an internal combustion engine.
In particular, it has been proposed to configure a hybrid vehicle in such a manner that allows a power storage device mounted on the vehicle to be charged by means of a power supply external to the vehicle (hereinafter also referred to as “external power supply”). There has accordingly been a demand for an increased distance over which these electrically powered vehicles can travel using the electric power stored in the vehicle-mounted power storage device. In the following, charging of a vehicle-mounted power storage device by an external power supply will also be referred to simply as “external charging”.
For example, Japanese Patent Laying-Open No. 2008-109840 (Patent Document 1) and Japanese Patent Laying-Open No. 2003-209969 (Patent Document 2) describe a power supply system having a plurality of power storage devices (batteries) connected in parallel. The power supply system described in Patent Document 1 and Patent Document 2 includes a voltage converter (converter) provided for each power storage device (battery) and serving as a charging/discharging adjustment mechanism. In contrast, Japanese Patent Laying-Open No. 2008-167620 (Patent Document 3) describes a power supply device in a vehicle mounted with a main power storage device and a plurality of sub power storage devices. The power supply device is configured to include a converter associated with the main power storage device and a converter shared by the plurality of sub power storage devices. This configuration can be employed to have a reduced number of device components and an increased amount of energy that can be stored.    Patent Document 1: Japanese Patent Laying-Open No. 2008-109840    Patent Document 2: Japanese Patent Laying-Open No. 2003-209969    Patent Document 3: Japanese Patent Laying-Open No. 2008-167620